iPhone上的OpenGL ES不会绘制任何内容

Question

我是iOS中OpenGL ES编程的绝对初学者。

这是我第一次尝试用OpenGL ES将一些简单的2D图元绘制到视图上。

这是类声明：

@interface OGLGameCanvas : UIView <GameCanvas> {
    EAGLContext* context;
    Game* game;
    GLuint framebuffer, renderbuffer, depthbuffer;
}

这是我的初始化代码：

- (void)initialize {

    // Get the layer and set properties

    CAEAGLLayer* layer = (CAEAGLLayer*)self.layer;

    layer.opaque = NO;
    layer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                            [NSNumber numberWithBool:NO], kEAGLDrawablePropertyRetainedBacking, kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];


    // Set the context

    context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES1];

    if (!context || ![EAGLContext setCurrentContext:context])
        DLog(@"Cannot create EAGLContext!");


    // Create the color buffer and the render buffer

    glGenFramebuffers(1, &framebuffer);
    glGenRenderbuffers(1, &renderbuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, renderbuffer);

    [context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer*)layer];
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, renderbuffer);

    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if (status != GL_FRAMEBUFFER_COMPLETE)
        NSLog(@"Failed to make complete frame buffer: %x", status);


    // Get width and height of the render buffer

    GLint width, height;
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &width);
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &height); 

    // Create and start animation loop

    CADisplayLink* displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(drawFrame:)];
    [displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

}

和我的绘图代码：

- (void)drawFrame:(CADisplayLink*)sender {

    glLoadIdentity();
    glClearColor(0.0, 0.0, 0.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glEnableClientState(GL_VERTEX_ARRAY);
    GLfloat vertices[] = { -20.0f, 2.5f, 0.0f, 0.0f, 1.5f, 7.5f };
    glVertexPointer(2, GL_FLOAT, 0, vertices);
    glColor4f(1.0, 0.0, 0.0, 1.0);
    glPointSize(5.0);
    glDrawArrays(GL_POINTS, 0, 3);
    glDisableClientState(GL_VERTEX_ARRAY);

    [context presentRenderbuffer:GL_RENDERBUFFER];

}

画布被清除（事实上，它变成黑色或红色，或者我设置为glClearColor的任何东西），但没有绘制点。

我很确定我忘记了一些基本和必要的东西。

谢谢你的帮助。

Answer 1

问题出在这里：

GLfloat vertices[] = { -20.0f, 2.5f, 0.0f, 0.0f, 1.5f, 7.5f };

标准化设备坐标位于[-1..1]范围内，因此您将它们绘制在可见区域之外。

和这里：

你必须在绘图之前这样做。

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();